1. Field of the Invention
The present invention relates to a belt drive apparatus and a belt drive method for correcting a position of a belt in a direction of a width of the belt.
2. Description of the Related Art
In an image forming apparatus using an intermediate transfer belt to convey a print paper, there may be a case where the intermediate transfer belt is shifted (displaced) in a direction of a width (hereinafter, a width direction) of the intermediate transfer belt while driving the intermediate transfer belt to travel. In such a case, the intermediate transfer belt travels while meandering. As a method of correcting a position of the intermediate transfer belt in the width direction by eliminating a shift or displacement, Japanese Laid-Open Patent Application No. 2004-271718 (hereinafter, Patent Document 1) suggests a method of controlling meandering of an intermediate transfer belt by inclining a roller supporting the intermediate transfer belt.
The Patent Document 1 also suggests providing an edge sensor, which detects a position of an edge of the belt, to detect an amount of meandering (a position in the width direction, hereinafter, a meandering amount) of the belt based on the detected position of the belt edge, and controlling an inclination of a roller for inclining (hereinafter, a steering roller) to maintain the meandering amount constant.
Moreover, the Patent Document 1 discloses, as a method of driving an intermediate transfer belt, a method of controlling a speed of the intermediate transfer belt based on a belt scale interval by detecting a plurality of lines of the belt scale provided on the intermediate transfer belt by a scale sensor. Hereinafter, this control is referred to as an intermediate transfer belt feedback control.
Further, the Patent Document 1 discloses a method of notifying, if an abnormality occurs in the belt scale or the scale sensor, of the abnormality in the belt scale or the scale sensor.
When performing both the above-mentioned belt width direction position control according to the steering method and the above-mentioned feed control of the intermediate transfer belt, the belt scale is arranged on only a part of the intermediate transfer belt (for example, a part along one side of the intermediate transfer belt in the width direction).
Moreover, at a time of replacing an intermediate transfer belt, there may be a case where the intermediate transfer belt is attached at a position apart from a reference position. FIG. 1 illustrates a state where the intermediate transfer belt 1 is displaced far away from the reference position. When the intermediate transfer belt 1 is displaced far away from the reference position, there may be a case where a scale sensor 44 cannot detect a belt scale 25 provided on the intermediate transfer belt 1.
FIG. 2 is a flowchart of a process according to a method of notifying of an abnormality in the belt scale 25 and the scale sensor 44. First, a drive operation of a drive motor for driving the intermediate transfer belt 1 is started to rotate the intermediate transfer belt 1 (step S2). Then, a CPU as a control part acquires an output signal of the scale sensor 44 immediately after the start of the drive operation of the drive motor. Thereafter, the CPU judges whether the output signal of the scale sensor 44 was changed within a fixed time (step S4). Here, the change in the output signal of the scale sensor 44 indicates that the scale sensor 44 is normally detecting (or reading) the belt scale 25.
If the CPU judges that the output signal of the scale sensor 44 was changed, that is, if the scale sensor 44 normally detected the belt scale 25 (YES of step S4), the CPU ends the process. On the other hand, if the CPU judges that the value (amplitude) of the output signal of the scale sensor 44 was not changed, that is, the scale sensor 44 did not normally detect the belt scale 25 (NO of step S4), a notification is sent that the belt scale 25 of the intermediate transfer belt 1 or the scale sensor 44 has an abnormality (step S6).
However, if the intermediate transfer belt 1 is displaced far away from the reference position as illustrated in FIG. 1, the scale sensor 44 cannot detect the belt scale 25. Accordingly, there may be a problem in that although there are no abnormalities in the scale sensor 44 and the belt scale 25, an abnormality of the scale sensor 44 or the belt scale 25 is notified because the scale sensor 44 cannot detect the belt scale 25.